To answer this question, we must first explain the Biblical idea itself. Father Ashley states that human persons are “beings who are at one time material and spiritual, and made in the likeness of God, who is pure spirit, but who is the Creator of matter and our body.” Far from an opinion, this conclusion is actually an article of Faith. Following the teaching of St. Thomas, the fathers of the Council of Vienne (1311-1312) declared that anyone who obstinately holds “that the rational or intellectual soul is not the form of the human body in itself and essentially, must be regarded as a heretic.”
This definition provides an example of how the Church uses Aristotelian hylomorphism to explain the contents of the Sacred Deposit. In the book of Genesis, we read that “the Lord God formed man of the slime of the earth: and breathed into his face the breath of life, and man became a living soul.” The natural philosophical conclusions of Aristotle perfectly complement this Biblical data. Man is a composite of body and soul, neither a Platonic-Kantian imprisoned angel, nor an Empiricist-Materialist walking computer. In the Catholic outlook, the soul needs the body and the body needs the soul for the completion of the human person.
Now we may consider what modern ideas about the relationship between body and soul have done to this outlook. Our considerations will articulate both negative and positive contributions.
Modern philosophical notions of body and soul are found seminally in “Descartes’ subject-object dualism. He split the human person into the material substance of the body and the spiritual substance of the mind.” Having thus torn asunder what God had joined together, Descartes paved the way for two distinct (and contradictory) trends in philosophy: On the Continent, the Idealism of Kant, which emphasized the soul at the expense of the body; in the Anglo-Saxon world, the materialistic Empiricism of men like Bacon, Locke, Hobbes, and Berkeley, which favored the body at the expense of the soul.
Kant’s idealism makes of man a rational soul trapped in a body whose senses are unreliable. While the spiritual faculties of intellect and will are capable of knowledge and appetition, the soul is hindered by the body. Held captive by this somatic incarceration, the mind watches (or produces) a film of something approximating the reality of the outside world. Kant advanced “the notion that the material world is a mental construction or at least that all we know of that world [are] the models that we impose on it.” By contrast, in philosophia perennis, the external senses of the body are assimilated by the internal senses (whose organ is the brain), which then supply the data to the super-organic faculty of the intellect. This process of abstraction, which, in the epistemological sphere, clearly shows the unity and interdependence of body and soul, has no counterpart in the idealist model of criteriology. Treating the soul as if it were a Manichean aeon held captive by evil matter, the idealist system makes the body a useless and harmful appendage.
The havoc that such a notion can produce in the realms of Christology, sacramental theology, and moral theology are well attested by such anti-Incarnational heresies as Gnosticism, Albigensianism, and the charismaticism of the disciples of Joachim of Flora. In dogmatic theology, Kantian epistemology has given us Rahner’s dangerous novelty of the “anonymous Christian.”
Anglo-Saxon materialism, on the other hand, chooses the opposite side of the Cartesian divide. The spiritual soul is nothing. The body as a complete substance has all it needs. The brain is the organ of thought which assembles sense data, forms judgments, and reasons. In short, we think with our brains. When taken to the extreme of Logical Positivism, this system reduces reason to a series of mathematical processes. Thus logic becomes, not the liberal art of philosophia perennis, but the mathematecist “symbolic logic” of George Boole, Bertrand Russell, and Alfred North Whitehead. In more recent times, the empiricists have posited that thought can be not only emulated, but actually achieved by non-living things, such as computers, thus giving us “artificial intelligence.”
In short, human knowledge - inasmuch as it is possible according to the various theories of the empiricists - begins and ends in the senses.
This position errs in depreciating the spiritual faculties. As we have said, the brain is the organ of the inner senses: memory, imagination, the estimative sense and common sense. These store and process the impressions made on the external senses. This process outlines the extent of the brain’s powers in relation to knowledge. After the brain has performed its necessary functions, the soul, with its reasoning power, takes over and abstracts truth.
Both sides of the Cartesian split, while being opposite errors, converge on the one great error of denying human knowledge. They have thus detracted from the greatest faculty in man, a faculty whose potency orders him to the Beatific Vision. On this theoretical score alone, therefore, it is not reactionary to say that modern ideas on the relation of body to soul have done great violence to the Biblical idea of the human person as a being created in the image and likeness of God.
Moving from theory to practice, we observe that the modern sciences become hopelessly entangled within the minutiae of their monistic web of secondary causality. “Such psychology tends to split into an emphasis on the study of the nervous system and the use of drugs in treatment of nervous disorders on the one hand or an emphasis on psychoanalysis, existential therapy, or cognitive therapy on the other.” Revelation gives us a much deeper and nobler understanding of the human person than either of these one-dimensional approaches.
As a positive contribution to the Biblical idea of the human person, modern scientific methodology, as long as its practitioners steer clear of scientism, can give us a deeper appreciation of the mechanism of the body. Since the human person is an integral composite of soul and body, any science which gains insight into the operations of either part can help us appreciate the whole: “The culmination of all the endeavors of natural science is [the] understanding of the human person.”
For example, Aristotle noted that our whole body manifests intelligence. From our possession of opposing thumbs to the placement of the highest external sense organs - the eyes - in a position maximized for the collection of sense data, everything about our bodies bespeaks intelligence. In disclosing to us the admirable design of the body, including the numerous complex electrochemical processes required to deliver sense impressions to the brain, scientific discovery has affirmed Aristotle’s insight.
It has also corrected some of the Peripatetic’s errors, which were based on the primitive biology and anatomy of his day. For instance, whereas Aristotle thought that the heart was the organ of the inner senses, we know (as has been stated already in this paper) that the brain performs that function. Thanks to the contribution of modern scientific research, we can now explain the body-soul relationship which we already knew by both faith and reason in these more refined terms: “We are created by God to share with Him the power of knowing the truth, of intelligence, and the freedom to be able to follow what is good and to avoid what is evil. In order to be able to do that, we have been given a body and that body has been organized in such a way that it serves our imagination, which is in our brain…. The brain is the instrument of our intelligence.”
But scientific method is limited. Just as Aristotle was capable of making mistakes by following the inadequate observations and conclusions of his day, modern scientists are capable of error, even while their capability to observe the human biological organism has expanded greatly.
As long as it uses the proper rules of induction and deduction given us by logic, and as long as it avoids the extremes of Empiricism and Idealism, modern science has before it a legitimate realm of discovery about the human person which is, secundum quid, virtually limitless. We say secundum quid, because all of the “big questions” have already been definitively answered by faith and reason. What remains is the lesser domain, expansive in its own right, of secondary causality. “We will never have a perfect knowledge of human nature. We are a mystery. They complexity of the human body, the depth of the human mind is so great that we can always learn more about ourselves. The standard definition of the human species as rational animals is a perfectly good definition, but we don’t know that much about our animal nature, and we certainly don’t know that much about our rational side. Theology works in this direction. Theology is aiming to understand the person as God made us, in all our complexity. It knows it will never come to an end, but it wants to know more. It is not content with old ideas about the human person. And on the other hand, it is confident that we do know enough about the human person from the ordinary experience of life, primary to science - the experimental and artificial observances of science - we know enough about ourselves to know who we are and to see ourselves as more than the animal, as beings who are at one time material and spiritual, and made in the likeness of God, who is pure spirit, but who is the Creator of matter and our body.”